Utility companies, specifically electricity generating and distributing utilities, must be able to generate sufficient power to serve the peak energy demand of their customers. It is well understood in the industry that the base demand is the least expensive energy to generate, while the peak demand can be the most expensive, requiring expensive peaking generators or the purchase of additional power from other utilities on a spot market. If the peak demand exceeds the capacity of the utility to generate or purchase electricity, the quality of the power provided can decline, resulting in brown-outs or load-shedding with involuntary black-outs to at least some of the utility's customers. One type of load shedding is the rolling blackout, where delivery of power to certain areas is cut off for shorter periods of time in an attempt to share the shortage over a wider base. These types of actions are necessary to maintain the quality of the power delivered to the remaining customers. Poor quality of delivered power can cause damage to expensive equipment of both the customer and the utility.
To address these problems, the utility can either increase generating capacity or reduce peak demand. Additional generating capacity is difficult and expensive to obtain, sometimes requiring the building of additional power plants. Regulatory delays and increased public opposition to the pollution and risks of new power plants has made this type of increase in capacity a long and expensive solution that is not practical for most utilities.
The less expensive and easier to implement solution to the problem is to reduce demand during peak periods through voluntary load shedding, where the power to some customers is voluntarily cut off. Voluntary load shedding has been attempted with public service pleas over the radio or television for customers to reduce their power consumption by raising the set-point on their air conditioner thermostats, closing their blinds to keep the sun out, or similar activities. For example, a residential power customer can use a set-back thermostat during the cooling season to raise the temperature of a residence during the day when the house is unoccupied, thus reducing power consumed and saving money. A set-back thermostat can be used to control an air conditioner, or a similar thermostat device used to control hot water heaters.
Other voluntary programs exist in which utility customers agree to allow the utility to reduce or eliminate power supplied during peak periods, usually with the incentive of reduced billing rates when enrolled in such programs. These programs can require action as dramatic as shutting down an entire factory, or as simple as shutting off a single residential air conditioner.
Other systems and methods of controlling energy usage and demand have also been developed. For example, U.S. Pat. No. 5,640,153 discloses an energy utilization controller and control system and method. Control data is transmitted from a remote location to a plurality of paging data receivers connected to respective energy management systems through a paging network and the energy management systems react depending on whether one or more predetermined addresses are within the control data.
U.S. Pat. No. 5,099,348 describes a display for remote receiver in a utility management system. Remote receivers in the utility management system are responsive to encoded command signals to perform utility control functions, such as removing electrical loads from the electrical distribution system or connecting a subscriber to a CATV system.
In U.S. Pat. No. 6,167,389, a control system is disclosed that varies the operation of consumer devices to minimize influx currents across a power grid. Power consuming devices are scheduled to operate in accordance with varying price tiers. The invention randomizes start up times of controlled devices so as to minimize the strain of the power grid as each one comes on line.
While the voluntary systems previously described offer some relief during peak demand periods and can be somewhat effective if a sufficient number of consumers participate, many residential customers then return to their residences and want their homes cooled down at exactly the time of the utility's peak power demand and at the time when the utility most wants to reduce demand. This is one reason the peak demand often occurs in the late afternoon, as the workday ends and utility customers return home. Another reason that the peak demand is in the late afternoon is that this can be the hottest part of the day.
Compliance with this type of voluntary load shedding has traditionally not been sufficiently effective enough to reduce demand and meet the short-term energy shortages thereby created. Further, the programs are slow to implement because of communication delays before power is cut off. For a utility to shut off 10,000 residential air conditioners would require the utility to manually or automatically send 10,000 commands to 10,000 individual customers. This process would not take place fast enough to successfully manage some peak load situations, for example when a transmission line or power generating plant goes off-line. Additionally, these systems are typically reactive and unpredictable, reducing peak demand only when there is an actual problem and making this type of load shedding extremely disruptive to each affected customer.
Therefore, a need remains in the industry for a high-speed, cost-effective, and reliable way to reduce peak power consumption through voluntary and utility-controlled load shedding.